5717bd39ee
When the output buffer is `NULL` with size 0, but the frame content size is non-zero, we will write to the NULL pointer because our bounds check underflowed. This was exposed by a recent PR that allowed an empty frame into the single-pass shortcut in streaming mode. * Fix the bug. * Fix another NULL dereference in zstd-v1. * Overflow checks in 32-bit mode. * Add a dedicated test. * Expose the bug in the dedicated simple_decompress fuzzer. * Switch all mallocs in fuzzers to return NULL for size=0. * Fix a new timeout in a fuzzer. Neither clang nor gcc show a decompression speed regression on x86-64. On x86-32 clang is slightly positive and gcc loses 2.5% of speed. Credit to OSS-Fuzz. |
||
|---|---|---|
| .. | ||
| .gitignore | ||
| block_decompress.c | ||
| block_round_trip.c | ||
| dictionary_decompress.c | ||
| dictionary_loader.c | ||
| dictionary_round_trip.c | ||
| fuzz_data_producer.c | ||
| fuzz_data_producer.h | ||
| fuzz_helpers.c | ||
| fuzz_helpers.h | ||
| fuzz.h | ||
| fuzz.py | ||
| Makefile | ||
| README.md | ||
| regression_driver.c | ||
| simple_compress.c | ||
| simple_decompress.c | ||
| simple_round_trip.c | ||
| stream_decompress.c | ||
| stream_round_trip.c | ||
| zstd_frame_info.c | ||
| zstd_helpers.c | ||
| zstd_helpers.h | ||
Fuzzing
Each fuzzing target can be built with multiple engines. Zstd provides a fuzz corpus for each target that can be downloaded with the command:
make corpora
It will download each corpus into ./corpora/TARGET.
fuzz.py
fuzz.py is a helper script for building and running fuzzers.
Run ./fuzz.py -h for the commands and run ./fuzz.py COMMAND -h for
command specific help.
Generating Data
fuzz.py provides a utility to generate seed data for each fuzzer.
make -C ../tests decodecorpus
./fuzz.py gen TARGET
By default it outputs 100 samples, each at most 8KB into corpora/TARGET-seed,
but that can be configured with the --number, --max-size-log and --seed
flags.
Build
It respects the usual build environment variables CC, CFLAGS, etc.
The environment variables can be overridden with the corresponding flags
--cc, --cflags, etc.
The specific fuzzing engine is selected with LIB_FUZZING_ENGINE or
--lib-fuzzing-engine, the default is libregression.a.
Alternatively, you can use Clang's built in fuzzing engine with
--enable-fuzzer.
It has flags that can easily set up sanitizers --enable-{a,ub,m}san, and
coverage instrumentation --enable-coverage.
It sets sane defaults which can be overridden with flags --debug,
--enable-ubsan-pointer-overflow, etc.
Run ./fuzz.py build -h for help.
Running Fuzzers
./fuzz.py can run libfuzzer, afl, and regression tests.
See the help of the relevant command for options.
Flags not parsed by fuzz.py are passed to the fuzzing engine.
The command used to run the fuzzer is printed for debugging.
LibFuzzer
# Build the fuzz targets
./fuzz.py build all --enable-fuzzer --enable-asan --enable-ubsan --cc clang --cxx clang++
# OR equivalently
CC=clang CXX=clang++ ./fuzz.py build all --enable-fuzzer --enable-asan --enable-ubsan
# Run the fuzzer
./fuzz.py libfuzzer TARGET <libfuzzer args like -jobs=4>
where TARGET could be simple_decompress, stream_round_trip, etc.
MSAN
Fuzzing with libFuzzer and MSAN is as easy as:
CC=clang CXX=clang++ ./fuzz.py build all --enable-fuzzer --enable-msan
./fuzz.py libfuzzer TARGET <libfuzzer args>
fuzz.py respects the environment variables / flags MSAN_EXTRA_CPPFLAGS,
MSAN_EXTRA_CFLAGS, MSAN_EXTRA_CXXFLAGS, MSAN_EXTRA_LDFLAGS to easily pass
the extra parameters only for MSAN.
AFL
The default LIB_FUZZING_ENGINE is libregression.a, which produces a binary
that AFL can use.
# Build the fuzz targets
CC=afl-clang CXX=afl-clang++ ./fuzz.py build all --enable-asan --enable-ubsan
# Run the fuzzer without a memory limit because of ASAN
./fuzz.py afl TARGET -m none
Regression Testing
The regression test supports the all target to run all the fuzzers in one
command.
CC=clang CXX=clang++ ./fuzz.py build all --enable-asan --enable-ubsan
./fuzz.py regression all
CC=clang CXX=clang++ ./fuzz.py build all --enable-msan
./fuzz.py regression all